1. Field of the Invention
The present invention relates to a heat treating oil composition, particularly a quenching oil composition. More particularly, it relates to a new type heat treating oil composition excellent in the stability at high temperature, suitable for quenching under the condition of a high oil temperature and capable of providing an object to be treated with excellent particularly in the initial phase of treatment with new oil, and long surviving brightness.
2. Description of Related Arts
Conventionally, a heat treatment, for example a quenching treatment has been given by feeding a metal heated to a high temperature into a quenching oil at 60.degree. to 150.degree. C. and quenching and hardening it. During the process of this quenching treatment, the metal preferably is quenched even at a higher oil temperature such as 170.degree. to 250.degree. C. to make the effective correction for a distortion.
However, conventionally known heat treating oils, for example those which are mixed with mineral oil, fatty acid, alkenyl succinimide and the like (Japanese Patent Applications Laid Open No. 4508/1977, No. 15913/1986, No. 106710/1986 and the like) have various problems that the stability at high temperature is poor, the life span of brightness is short, or the like. Meanwhile, inferior brightness has been blamed as one of the reasons for an increase of distortion associated with quenching.
On the other hand, the heat treating oil can have the improved stability at high temperatures by comprising a highly purified base oil. It has been known, however, that resulting in an increase of inferior brightness, quenching unevenness and quenching distortion.
Moreover, a marquenching treatment (at a liquid temperature closely above the Ms point of the object to be treated, that is, usually 160.degree. to 250.degree. C.) using salt has also been known as suitable for decreasing the quenching distortion. But this treatment has been found to have poorer working efficiency than that of quenching oil, accompanied even by environmental problems.
Thus, the present inventors have made intensive studies with a view to finding a solution in these problems and developing a heat treating oil composition capable of quenching at high oil temperatures and obtaining a treated metal having excellent brightness and free of the distortion.
As the result, it has been found that said objects can be achieved by a heat treating oil composition comprising a base oil consisting of a highly purified mineral oil or synthetic oil and a specific content of sulfur, along with various additives for quenching. The present invention has been completed on the basis of this finding.